1. Field of the Invention
The present invention relates to a feed antenna (planar antenna) including a dielectric waveguide. The feed antenna works at high frequencies higher than those of millimeter waves with high efficiency and is small in size and suitable for large-scale manufacture.
2. Description of the Related Art
Among antennas working at high frequencies higher than those of submillimeter waves, known is a dielectric leaky-wave antenna which includes a dielectric waveguide including a grounding conductor and a dielectric plate placed thereon, metal strips arranged on the dielectric plate at predetermined intervals, and transmission lines from which electromagnetic waves leak. When such a dielectric leaky-wave antenna has an array structure in which a plurality of slim transmission lines are arranged in parallel, wide-band plane waves of which the planes are parallel to each other must be fed in the direction in which the transmission lines are arranged.
Known dielectric lenses and parabolic reflectors used to generate such wide-band plane waves are large in size and are not therefore suitable for small-sized systems such as millimeter-wave radar systems for on-vehicle use.
Spaces or dielectric members with different dielectric constants must be three-dimensionally arranged to in dielectric waveguides or metal plates or metal strips must be placed on side faces of dielectric waveguides in the longitudinal direction. Therefore, there is a problem in that known feed antennas cannot be manufactured with low cost and are not suitable for large-scale manufacture because of their complicated structures.